Was Imam Zaman's (as) mother Nargis, the daughter of a Roman king, or a maid from the region of Sudan? Are there different opinions abut this matter and which scholars subscribe to each?
Both views are narrated. The story that she was the daughter of a Roman (Byzantine) king tends to be more popular, possibly because it is a more developed and engaging story.
This book offers a good discussion of the question. As you can see, it argues against the idea that she was a Roman princess on historical grounds.
https://www.al-islam.org/occultation-twelfth-imam-historical-background-...
Allah knows best.